In contemporary communication systems it is known to transmit useful data, e.g. for voice, video or multimedia communication, via packet-oriented networks. The use of packet-oriented data transmission methods often results in losses in the quality of the useful data to be transmitted, said losses frequently being due to conversions and delays of useful data packets by network nodes.
In conformity with the widely used “Internet Protocol”, also referred to in its abbreviated form as IP, the term “IP terminal device” will also be used in the following to refer to communication terminals which operate on the basis of a packet-oriented transmission technology. In the packet-oriented transmission of useful data the term “Voice over IP”, VoIP for short, is also common currency. In this case the ITU-T (International Telecommunication Union—Telecommunications Standardization Sector) recommendation H.323 or, as the case may be, the SIP (Session Initiation Protocol) protocol developed by the IETF (Internet Engineering Task Force) working group is widely established for VoIP communication.
Devices known as gateways are used for converting between circuit-oriented and packet-oriented transmission technologies, said gateways often being disposed in each case between a packet-oriented network and a communication equipment operating according to a circuit-switching method. In this case the gateways include means for mutual conversion of data streams into data packets. At the same time this conversion relates to both signaling data and useful data, which is to say in particular voice, video data or also nonverbal useful data such as, for example, audio signals of telecopier units or modems. The useful data is also referred to in technical circles as “payload”.
As part of a more general description the term “connection controller” will also be used in the following for gateways, known as gatekeepers, as well as for devices which are involved as independent units in a call setup or in call switching in addition to the aforementioned units. Said connection controllers enable signaling information and payload to be exchanged between IP terminal devices during a call setup or when a connection has been established. In this case both this signaling information and the payload are frequently routed via the connection controllers.
A communication system is often characterized by being structured into individual subnetworks, with each subnetwork typically being managed by a communication equipment. In order to transmit useful data or signaling data, the communication equipments often operate according to different transmission methods or transmission protocols, depending on the necessary packet-oriented or circuit-oriented connection equipment type of the connected communication terminals.